[Tychon] Clean up for review

[chrisberkhout]

Miscellaneous clean-up for review.

### Tasks
- [ ] Is the CMRS data stream useful? Test data has large base64 encoded XML data in it, not touched by the pipeline
- [ ] Ensure we have some test data for external_device_control
- [ ] Add "preserve original event" option for the CMRS data stream
- [ ] Set correct initial version number and changelog entry
- [ ] Add screenshots
- [ ] Mark as partner supported
- [ ] Tidy/remove any additiona/unnecessary assets in kibana/
- [ ] Use modern ECS
- [ ] Ensure tychon_external_device_control collects from linux paths, if only for testing
- [ ] Consolidate docker-compose.yml (2 versions, should be 1), stream.yml.hbs (3 versions, should be 2)
- [ ] Assert hit counts in system tests
- [ ] Review and update README
- [ ] Reivew and update descriptions that appear on the add policy page
- [ ] Review categorizations in manifest files and ECS fields
- [ ] Ensure publisher_pipeline.disable_host and perserve_duplicate_custom_fields agent options are used appropriately
- [ ] Remove any data streams or other elements that should be postponed until after the initial merge

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)